Granulated crystalline plastic bonded explosives



Jan. 3, 1967 S. B. WRIGHT GRANULATED CRYSTALLINE PLASTIC BONDED EXPLOSIVES BINDER Filed July 8, 1964 v /2 EXPLOS/VE [J6 SOLVENT //4 GRANULA T0,?

/8 F/L TEE '20 DRYER SAM B. WRIGHT INVENTOR BY M ATTORNEYS United States Patent O This application is a continuation-in-part of my copending applications Serial No. 234,467, now Patent No.

3,173,817, filed October 31, 1962; Serial No. 203,079,

now Patent No. 3,138,501, filed June 18, 1962; and Serial No. 50,311, filed August 18, 1960.

This invention relates to the manufacture of explosive compositions. More particularly, it relates to a method of granulating plastic-bonded explosives.

Water-insoluble plastic-bendable explosives include DATB (diaminotrinitrobenzene), RDX (cyclotrimethylenetrinitramine, cyclonite, Hexogen), HMX (cyclotetramethylenetetranitramine, homocyclonite, Octogen) and the like. Known methods of making such explosive-s include dispersion of the explosive in a water-miscible solvent solution of a binder followed by precipitation of the binder by addition of quench water or a precipitating agent and pressure extrusion of a plasticized binder followed by incorporation in the explosive as small lumps. In these procedures difficulties are sometimes encountered in producing a product of sufliciently high particle and bulk density and particle uniformity to be acceptable for most explosive uses. The production of a high bulk density plastic-bonded explosive of optimum granule size, porosity and texture in a minimum number of substantially trouble-free steps therefore represents a highly desirable result.

One object of the present invention is to provide a plastic-bonded explosive of maximum bulk density and optimum granulation characteristics. Another object of this invention is to provide a method of producing a plastic-bonded explosive of enhanced bulk density and increased uniformity of dispersion of the explosive. A further object is to provide a method of preparing an explosive molding powder of especially high bulk density. These and other objects will be apparent hereinafter.

In its broader aspects, my invention involves a plasticbonded explosive containing 2 to 50 percent by weight of an elastomeric binding material, the explosive being a cap-sensitive crystalline high explosive such as an organic nitrate or nitramine. The binding material or bonding agent should be dispersible in a liquid medium and chemically inert with the system in which used. According to preferred embodiment at least about 0.5 percent of a strengthening ingredient such as polyester fiber, metallic fines or the like is included in addition to the binding material. A binder solvent may be used in coating the binding material or binder substantially uniformly over the surface of granules preferably of a waterinsoluble plastic-bondable explosive. The explosive may be slurried in water. In one embodiment an aqueous dispersion of the binder is mixed with the water slurry of explosive and an organic solvent in which the binder is soluble added to the system after precipitation of the binder onto the explosive by addition of a coagulant such as alum, acetic acid, acetone, or gelatin. In another embodiment the binder solvent is used to make a solution of the binder which is mixed with the water slurry of explosive to yield globules of explosive/ binder, using in addition a protective colloid such as gelatin, polyvinyl alcohol, gum arabic or the like for controlling particle size, if desired. In both of these procedures the solvent is removed by distillation to provide hardened granules ing, soluble-type), as binder.

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which are then separated, for example, by filtration, and dried. The binder is an organic resinous thermoplastic polymer such as polyamide, polyacrylate, polyisobutylene, polytetrafluoroethylene or a copolymer of chlorotrifluoroethylene or hexafluoropropylene and vinylidene fluoride. Representative of binder solvents which may be used are isobutyl acetate, isobutyl alcohol, butyl acetate, methyl ethyl ketone, butyl alcohol, benzyl alcohol, toluene, xylene and the like. The solvent may also consist of a mixture of more than one of such solvents.

In a further embodiment my invention involves the use of a water-immiscible solvent, preferably benzyl alcohol, butyl alcohol or toluene in forming a high-bulk plasticbonded explosive, viz., DATB, HMX, RDX or a mixture of two or more of these three, with an organic resinous thermoplastic polymer, preferably polyamide (low meltbutyl alcohol. As indicated hereinabove, the solvent may be used to form a solution of the binder prior to addition to a water slurry of the explosive or after addition of an aqueous dispersion of the binder to a water slurry of the explosive, preferably after granulation by addition of a coagulant. A plasticizer or other appropriate viscosity or consistency-regulating substance (e.g., motor oil) may be used in conjunction with the binder.

For a more complete under-standing of my invention reference is made to the attached drawing which is a part hereof and illustrative of the process of my invention. The drawing is in schematic flow sheet form.

In the drawing, the binder 10 is added to the water slurry of the explosive 12 to form a mixture which is granulated at 14, the solvent being removed at 16 by evaporation. The product is then filtered at 18 and dried at 20 to high-bulk plastic-bonded explosive granules.

The following examples are illustrative of my invention but are intended to be representative only and not limiting.

Example I Prepare a polyhexamethylene adipamide/butyl alcohol lacquer by dissolving 20 to 50 g. polyamide in 500 g. butyl alcohol at 65-75" C. Place 2,000 g. water and 470 g'. diaminotrinitrobenzene (DATB) in a IO-liter still. Adjust agitation to 500600 rpm. and heat the slurry to 70-75 C. Add the lacquer solution to the agitated slurry at a rate suflicient to insure incorporation into the explosive/water slurry. The resulting emulsion is agitated until the desired granule size is obtained. The butyl alcohol is vaporized to yield a hardened granule. The slurry is cooled to about 50 C. and filtered. The resulting product contained about 2-10 percent polyhexamethylene adipamide and about 98-90 percent DATB. The bulk density of the product was about 0.6 to 0.7 gm./ ml. The granules were hard and well formed. The granulation was essentially 100 percent passing U.S. Sieve No. 18 and essentially 100 percent retained on US. Sieve No. 80. The granules were pressed into pellets (0.9" dia. x 1" long) at 25,000 p.s.i.g. and C. to yield a density of greater than 95 percent of the calculated or theoretical density; the compressive strength was greater than 10,000 p.s.i.

Example II The procedure of Example I was followed except that benzyl alcohol was used in place of butyl alcohol. Granules comparable to those of Example I were pressed into 0.9" x 1" pellets having a density of about 96 percent of the theoretical.

Example III A separate batch of plastic-bonded explosive was prepared. The procedure of Example I was followed ex- The preferred solvent is 1 cept that about 0.1 percent gelatin, based on product Weight, was added to the mixture during granulation and the explosive used this time was RDX.

Example IV Slurry 470 g. DATB and 4,000 g. water in a -liter still. Add 200 to 500 g. polyhexamethylene adipamide dispersion (10 percent polyhexamethylene adipamide). Mix well and adjust agitation to 300-400 r.p.m. Coagulate the polyhexamethylene adipamide by adding 2 to 3 g. acetic acid dissolved in 100 ml. water. Add 500 ml. butyl alcohol and digest at 30 to 40 C. for to 30 min. Vaporize the butyl alcohol from the system. Cool the batch and filter. The product containing 2-10 percent polyamide and 98-90 percent DATB exhibited characteristics comparable to those cited for the product prepared with a lacquer of polyhexamethylene adipamide and butyl alcohol.

Example V Another batch of explosive product was formed using the procedure of Example IV except that about 0.1 percent poly(vinyl alcohol), based on product weight, was added to the mixture during granulation and the explosive used was HMX.

Example VI Lacquer preparation.Add 12.5 grams polyisobutylene, precut to marble size, to 130 grams toluene. Agitate the mixture at 6070 C. for 1 /2 hours. Add 8.0 grams motor oil (SAE 10) and 29.5 grams di-(2-ethylhexyl) sebacate and mix well. Cool to 30 C.

Granulation.Add 5 liters of Water to a 10-liter granulator, adjust agitation and add 150 grams of fine RDX (about 3 percent retained on USS No. 325 sieve) and 300 grams of coarse RDX (about 50 percent retained on USS No. 100 sieve). Add 0.1 gram gelatin and heat the slurry to 65 C. Add the lacquer over a 1 to 2 minute period with agitation set at 450 to 500 r.p.m. Heat the mixture to 99.5 to 100 C. Cool the slurry to 60 C. Transfer the slurry to a vacuum filter, remove the water. Dry the product at 50-60 C., using a forced air dryer, for 2 /2 hours.

Results: Percent added RDX, percent89.90 90.0 Binder, percentl0.09 10.0

Water, percent-0.01

Binder content:

2.68 percent polyisobutylene. 7.41 percent oil di(Z-ethylhexyl) sebacate. Plasticity=0.004 unit.

Example VII The lacquer was prepared as discussed in Example VI with the exception that 170 grams toluene were used.

Granulali0n.Add 505 grams RDX (2 parts coarse RDX and 1 part fine RDX) to 5.5 liters of water in a 10- liter granulator. Add 0.2 gram gelatin and heat the mixture to 75 C. The lacquer addition and solvent removal is made according to the procedure of Example VI.

The product was dried at room temperature, 25 to 30 C., by placing the material in open trays. The depth of the material was about /2 inch.

Results: Percent added RDX, percent90.60 91.0 Water, percent0.17.

Binder, percent9.23 9.0

Binder content:

2.33 percent polyisobutylene 2.25 6.90 percent oil di(Z-ethylhexyl) sebacate 6.75

Example Vlll This batch was processed as discussed under Example V with the exception that the amount of toluene was in- 4 creased to 200 grams and the amount of water for the RDX/water slurry was reduced from 5 liters to 2 liters.

Example IX Binder preparati0n.-Add 4.55 liters toluene to a 10- liter still. Heat to 70 C. Add 254.3 grams polyisobutylene, cut in small pieces to facilitate dissolution, and reflux the solvent until solution of the binder is obtained. Cool the solution to 30 C., add 603.8 grams di(2-ethylhexyl) sebacate and 174.8 grams motor oil (SAE 10). Mix well and transfer the binder to a five-gallon safety can. Prepare two binder batches, as described above, for a 50 pound batch of a composition containing 61 percent coarse RDX, 30 percent fine RDX, 2.25 percent polyisobutylene, 5.31 percent di-(2-ethylhexyl) sebacate and 1.44 percent SAE 10 motor oil.

Granulati0n.-Add 400 pounds water and 30.5 pounds coarse RDX and 15.0 pounds fine RDX to the granulator. Add 0.01 pound dry gelatin and heat the slurry to 75 to C. Add the prepared lacquer at a rate of about /2 gallon per minute. Set agitation at 250 rpm. and heat the slurry to 99 to 100 C. Cool the batch to 50 to 60 C. and drop the material to a vacuum filter. Dry a portion of the product by the following methods: rotary vacuum dryer at 60 C., forced air dryer at 60 to 70 C., and an incorporation kettle at C.

Results: Percent added RDX, percent90.90 91.0 Binder, percent-8.97 9.0 Water, percent0.18.

Plasticity-0.004 unit.

Specific gravity1.65 g./ml.

Example X Binder preparation.Prepare the binder, in a production scale lacquer pot, according to the method described in Example IX. Use the following amount of materials.

Pounds Polyisobutylene 56 Di(2-ethylhexyl) sebacate 133 Motor oil (SAE 10) 39 Toluene 850 Granulati0n.The material was granulated according to the procedure outlines in Example IX. A production scale granulator was used. Material usedcoarse RDX, 1525 pounds; fine RDX, 750 pounds; water, 20,000 pounds; gelatin, 0.5 pound.

Results: Percent added RDX, percent-91.03 91.0 Binder, percent-8.97 9.0 Water, percent0.06.

Insolubles, percent-None. Plasticity-0.010 unit.

Specific gravity, g./ml.1.60.

Example XI Slurry 425 g. HMX and 2,000 g. water in a 10 liter still. Add 150 g. poly(ethyl acrylate) latex (50 percent solids) and agitate the mixture for about 5 min. Add 3 g. alum dissolved in about 30 g. water. Heat the slurry to about 99 C. to remove volatiles added to the system with the poly(ethyl acrylate) latex. Cool the material to 50 C. and filter. Granulation of the material was essentially 100 percent passing U.S. Sieve No. 18 and about percent retained in US. Sieve No. 100. Bulk density of the material was about 0.6 to 0.7 g./ml.

Example XII Slurry 510 g. HMX and 2,000 g. water in a liter still. Add 180 g. dispersion of chlorotrifluoroethylenevinylidene fluoride copolymer (50 percent solids) and agitate the mixture for min. Add 3 g. alum dissolved in 30 g. water. Heat the slurry to 80 to 82 C., add 115 to 125 g. isobutyl acetate and 1 to 2 g. poly (vinyl alcohol). Heat the mixtureof 99 C. Cool to 40 C. and filter.

The product exhibited a bulk density of 0.97 g./ml. and granulation of 100 percent passing U.S. Sieve No. 4 and 100 percent retained on US. Sieve No. 40.

Example XIII Slurry 425 g. HMX and 2,000 g. water in a 10 liter still. Add 125 g. polytetrafluoroethylene dispersion (50 percent solids). Agitate the slurry for 5 to 10 min. Add 160 ml. n-butyl acetate. Add 1.5 liters acetone over a 2 to 5 min. period. Agitate the mixture for about 5 min. Filter the granulated product. Granulation of the material was essentially :100 percent passing U.S. Sieve No. 18 and essentially 95 percent retained of US. Sieve No. 50. Bulk density of the product was about 0.6 g./ml.

Examples XIV-XVI The procedures of Examples XI-XIII respectively were followed except that in each case RDX was used in place of the HMX. In every instance the product was of substantially the same properties given for the corresponding plastic-bonded HMX.

Example XVII The procedure of Example XIII was followed except that a 1,000 g. dispersion of polyamide (50 percent solids) containing 500 g. polyamide was used in place of the .125 g. polytetrafluoroethylene. A high density plastic-bonded explosive was produced.

Example XVIII A composition containing 59.5 percent by weight of HMX, 0.5 percent polyester fiber and 40 percent by weight of polytetrafiuoroethylene resin was prepared as follows: The HMX (0.595 part) and polyester fiber (0.005 part) were slurried in about twice their weight of water. Polytetrafiuoroethylene resin (0.40 part) was dispersed together with about 1.35 percent of a non-ionic wetting agent based on the weight of the polytetrafluoroethylene resin in sufficient water to make a substantially homogeneous dispersion having a total polytetrafluoroethylene resin solids content of from about 33 percent to about 35.5 percent by weight, a pH of about 10, a room temperature viscosity of about 4 oentipoises, and a density of from about 2.1 to about 2.3 g./ml. This dispersion was added slowly to the slurry of HMX. About 3 parts by weight of acetone based upon the expected total product weight were then added slowly, and the dispersion was mixed with increased agitation for about two minutes. The thoroughly mixed dispersion was then vacuum filtered and dried. The molding powder which resulted was of a fluffy and tacky texture. It was compacted with rolls in a conventional manner into sheet form. The molding powder was pressed under about 5 mm. Hg vacuum into cylindrical pellets of about /2 inch in diameter and inch to 1 inch in height at a temperature of from about 120 C. to about 125 C. and at a pressure of from about 20,000 p.s.i. to about 30,000 p.s.i. The density of the pellets produced was from about 97 percent to about 99 percent of the theoretical maximum density.

From the foregoing description it is thought apparent that I have provided a novel plastic-bonded explosive of increased bulk density and uniformity of distribution of explosive particles.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

I claim:

1. A plastic-bonded high-density explosive molding composition comprising about from to 98 percent by weight of cap-sensitive, crystalline high explosive selected from the group consisting of organic nitrates and nitramines and about from 2 to 50 percent by weight polyester, polyamide or polytetrafluoroethylene binding material therefor, said binding material being dispersible in water, and chemically inert with the system, said composition being in the form of granules of a size such that substantially 100 percent pass a US. Sieve No. 18 and substantially 100 percent are retained on a US. Sieve No.80.

2. The composition of claim 1 wherein the explosive is RDX, HMX, or DATB.

3. The composition of claim 1 containing additionally at least about 0.5 percent of a strengthening ingredient.

4. The composition of claim 3 wherein the strengthening ingredient is polyester fibers or metallic fines.

References Cited by the Examiner UNITED STATES PATENTS 2,999,743 9/1961 Breza et a1 149-19 3,006,957 10/1961 Murray et al. 149-92 X 3,116,186 12/1963 Paul 149-92 X 3,117,044 l/1964 Sauer 149-92 X 3,173,817 3/1965 Wright 149-92 X 3,227,588 1/1966 Jones et al. 149-19 BENJAMIN R. PADGETT, Primary Examiner. 

1. A PLASTIC-BONDED HIGH-DENSITY EXPLOSIVE MOLDING COMPOSITION COMPRISING ABOUT FROM 50 TO 98 PERCENT BY WEIGHT OF CAP-SENSITIVE, CRYSTALLINE HIGH EXPLOSIVE SELECTED FROM THE GROUP CONSISTING OF ORGANIC NITRATES AND NITRAMINES AND ABOUT FROM 2 TO 50 PERCENT BY WEIGHT POLYESTER, POLYAMIDE OR POLYETRAFLUOROETHYLENE BINDING MATERIAL THEREFOR, SAID BINDING MATERIAL BEING DISPERSABLE IN WATER, AND CHEMICALLY INERT WITH THE SYSTEM, SAID COMPOSITION BEING IN THE FORM OF GRANULES OF A SIZE SUCH THAT SUBSTANTIALLY 100 PERCENT PASS A U.S. SIEVE 18 AND 